As device geometries continue to decrease in electronics and optoelectronics, capacitance density will increase and the performance of integrated circuits will be limited by the high RC time constants caused by high resistivity metals and high capacitance interlevel dielectrics (ILD). Reducing the dielectric constant of the interlevel insulator will not only enhance performance, but also decrease the power consumption and crosstalk of electronic/optoelectronic devices.
For a given interconnect layout, both power dissipation and crosstalk decrease as the dielectric constant of the insulator decreases. FIG. 1 shows the power dissipation of 0.25 .mu.m and 0.50 .mu.m metal lines when different ILDs are used. The data show that using the same dielectric, scaling down from 0.50 .mu.m to 0.25 .mu.m will result in a 30% increase in power dissipation. The power dissipation can be decreased more than 50% if SiO.sub.2 ILD is replaced by a copolymer made from tetrafluoroethylene and 2,2-bis(trifluoromethyl)-4,5-difluoro-1,3-dioxole (TFE AF). (TFE AF is commercially available from DU PONT.TM. in a product known as amorphous TEFLON.TM.; TEFLON.TM. is a polymer made from polytetrafluoroethylene (PTFE) also commercially available from DU PONT.TM.). This change is particularly important for high frequency operation because power dissipation increases proportional to frequency. The power consumption can be further reduced if a metal of lower resistance, such as Cu, is used to replace current metalization materials such as Al or W.
FIG. 2 shows the crosstalk between 0.25 .mu.m and 0.5 .mu.m metal lines when the power supply voltage (V.sub.cc) is 1 V. The crosstalk increases more than 50% when the design rule is reduced from 0.5 .mu.m to 0.25 .mu.m, primarily due to the increase in line-to-line capacitance. The increase in crosstalk/V.sub.cc ratio degrades the noise margin and hence circuit performance. Replacing SiO.sub.2 by TFE AF will significantly reduce crosstalk.
Several material properties are required for a successful low-.epsilon..sub.r technology. These include: 1) low dielectric constant, 2) high mechanical strength, 3) good thermal stability, 4) high dielectric strength and low leakage current, 5) low stress, 6) good adhesion, 7) good gap filling capability/ease of planarization, 8) ease of pattern and etch, 9) low water absorptivity, 10) good etch selectivity to metal and 11) good thermal conductivity. A list of a few important properties of TFE AF, PTFE and SiO.sub.2 are given in Table 1. The properties of PTFE and SiO.sub.2 are listed for comparison.
TABLE 1 ______________________________________ Requirements TFE AF PTFE SiO.sub.2 ______________________________________ Dielectric Constant 1.9 2.1 3.5-4.0 Dissipation Factor &lt;0.00035 &lt;0.0002 0.001 Stable Temperature 360.degree.C. 380.degree.C. 1600.degree.C. Creep Resistance good poor good Resistivity (ohm-cm) &gt;10.sup.18 &gt;10.sup.18 &gt;10.sup.14-17 Dielectric Strength 0.2 (MV/cm) 1.3 5-8 Thermal Conductivity 0.012 Chemical Resistance excellent excellent Water Absorption &lt;0.01% &lt;0.01% ______________________________________
No single polymer exhibits all of the required characteristics. TFE AF has the lowest dielectric constant in known polymers. In addition, TFE AF has processing advantages.
Unlike PTFE, which is formed by molding, TFE AF can be deposited as a thin film by either spin-coating, thermolysis or laser ablation. This makes it more applicable to integrated circuits. TFE AF exhibits better creep resistance, a lower dielectric constant, lower thermal expansion and higher tensile strength than PTFE. Good chemical resistance and low water absorption are common for both materials.